Release films have been used in a wide variety of applications. For example, release films are used as protective coversheets for photosensitive materials, as release layers for pressure sensitive adhesives, as temporary supports for decorative decals and stickers, etc. Typically, such release films comprise a polymeric film substrate coated with a silicone release layer. The silicone release layer is generally a coating of a cured, i.e., crosslinked, polysiloxane resin. While such coatings exhibit good release properties, the anchorage of the silicone resin to the polymeric film substrate has been found to be unsatisfactory. In extreme cases, where the silicone composition is cured under conditions of high humidity, the resultant layer is readily removed when rubbed with one's fingers.
The adhesion of the silicone resin to the film substrate is often improved by applying a surface treatment to the substrate prior to coating the silicone resin. Surface treatments which have been used include treatment with a flame or a corona discharge. However, there are variations in the strength of such surface treatments and, therefore, a reliable level of adhesion is not always obtained. In addition, in some cases when the silicone-coated film substrate is stored in the form of a continuous roll, some of the silicone transfers to the backside of the film.
EPO application 416,765 A2 published Mar. 13, 1991, describes a release film comprising a self-supporting, polymeric film substrate having on at least one surface thereof, a polymeric abherent layer wherein the abherent layer comprises a polyurethane resin which is the reaction product of (i) an organic polyisocyanate, (ii) an isocyanate reactive polydialkylsiloxane, and (iii) a polymeric polyol. The abherent layer adheres firmly to the film substrate but provides release from an opposing surface.
It would be desirable to obtain a release film that exhibits reliable and improved adhesion between the substrate and the silicone release layer as well as little or no back transfer of the silicone during storage. These needs are met using the release film of the invention.